Mask



FIG. 1 is a front view of a mask according to our new ornamental design;

FIG. 2 is a rear view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a bottom view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a right side view thereof; and,

FIG. 7 is an exploded front perspective view thereof in a condition in which the positions of the swivel elbow and plug have been interchanged.

The broken lines show structure that forms no part of the claimed design. The dotted lines show the boundary between claimed and unclaimed subject matter and form no part of the claimed design.

The illustration of stitching in the figures forms part of the claimed design. 

CLAIM The ornamental design for a mask, as shown and described. 